Nitrogen fixation in red clover grown in multi-species mixtures with ryegrass, chicory, plantain and caraway

Summary

While many studies have investigated effects of species composition and management on N2-fixation dynamics in simple clover-grass mixtures, there is a lack of knowledge about the performance of legumes and their N2-fixation in more species-rich grassland including non-legume forbs. This study investigated N2-fixation and total N yield in grassland mixtures including different combinations of red clover, perennial ryegrass and three deep rooted forbs: chicory, ribwort plantain and caraway, managed without and with slurry application. The percentage of clover N derived from atmosphere (%Ndfa) increased in mixtures, but was unaffected by inclusion of forbs. However, forbs affected the quantity of N2-fixation and total N yield by affecting the red clover proportion in the mixtures. Mixtures composed of grass,clover and plantain or caraway showed higher N2-fixation and N yield than with chicory included. Slurry application reduced N2-fixation due to decreasing clover contents in the sampled biomass. The study highlighted differences among forbs in their influence on legume N2-fixation and total N yield showing that forbs can be included in grasslands without negative effects on red clover performance.